It concerns manufacturing a low-resistance electrical contact between a current lead, generally made of copper, and a high critical temperature superconductive ceramic, of the type RBa.sub.2 Cu.sub.3 O.sub.y, where R designates a lanthanide chosen from Y, La, Nd, Sm, Eu, Gd, Ho, Er, Tm, Yb, and Lu, and where y lies in the range 6.9 to 7.
Such a contact must allow high currents of the order of at least 1,000 A, and/or high current densities to flow therethrough.
The publication "YBaCuO current lead for liquid helium temperature applications" by F. Grivon et al. 1990 Applied Superconductivity Conference--Snowmass Colo., 24-28 Sept 90, mentions the following method.
A brush is used to apply a paint based on a silver-containing epoxy resin to a part made of a YBaCuO ceramic. After the painted part has been dried, it is subjected to heat treatment at high temperature in oxygen using the following cycle:
heating to 800.degree. C. at a rate of 60.degree. C. per hour; PA1 heating to 930.degree. C. at a rate of 10.degree. C. per hour; PA1 maintaining the temperature stable for 6 hours; PA1 cooling to 450.degree. C. at a rate of 30.degree. C. per hour; PA1 maintaining the temperature stable at 450.degree. C. for 12 hours corresponding to the phase during which the ceramic is reoxygenated; and PA1 cooling to ambient temperature at a rate of 30.degree. C. per hour.
Among the results given in the above-mentioned publications, the lowest contact resistance per unit area measured at 77K is 1.7.times.10.sup.-11 .OMEGA..m.sup.2 with a current of 550 amps.
An aim of the present invention is to provide a contact offering improved performance for even higher currents or current densities.